Biologics and cardiac disease: challenges and opportunities
Authors: Giulio Ciucci, Andrea Colliva, Roman Vuerich, Giulio Pompilio, Serena Zacchigna
Journal: Trends in Pharmacological Sciences (2022)

Cardiovascular diseases represent the leading cause of death globally. However, biological drugs, which stand to be real gamechangers in other medical sectors such as cancer and immune and genetic diseases, struggle to enter the cardiovascular field.Biological drugs, or biologics, are medicinal products that are produced from living organisms and include recombinant proteins, gene therapy, and cell therapies. Their manufacture is far more complex than small-molecule drugs.Specific features of cardiac diseases may represent a challenge for the successful application of biologics in clinical settings. Overcoming these challenges may offer unprecedented opportunities to radically change the toolbox of drugs to treat cardiac diseases, with obvious societal and economic implications. Biologics are revolutionizing the treatment of chronic diseases, such as cancer and monogenic disorders, by overcoming the limits of classic therapeutic approaches using small molecules. However, the clinical use of biologics is limited for cardiovascular diseases (CVDs) , which are the primary cause of morbidity and mortality worldwide. Here, we review the state-of-the-art use of biologics for cardiac disorders and provide a framework for understanding why they still struggle to enter the field. Some limitations are common and intrinsic to all biological drugs, whereas others depend on the complexity of cardiac disease. In our opinion, delineating these struggles will be valuable in developing and accelerating the approval of a new generation of biologics for CVDs. Biologics are revolutionizing the treatment of chronic diseases, such as cancer and monogenic disorders, by overcoming the limits of classic therapeutic approaches using small molecules. However, the clinical use of biologics is limited for cardiovascular diseases (CVDs) , which are the primary cause of morbidity and mortality worldwide. Here, we review the state-of-the-art use of biologics for cardiac disorders and provide a framework for understanding why they still struggle to enter the field. Some limitations are common and intrinsic to all biological drugs, whereas others depend on the complexity of cardiac disease. In our opinion, delineating these struggles will be valuable in developing and accelerating the approval of a new generation of biologics for CVDs. Biological drugs, or biologics, are medical products that are produced from living organisms or contain their components. They mainly include recombinant proteins, gene therapy and cell therapy products. Because their manufacture requires the use of living cells or organisms, their production is much more complex and expensive than that of the majority of chemical drugs and small molecules, which constitute >90% of the current pharmacopeiai. Despite this major drawback, the number of biologics approved by the FDA has constantly risen over the past 12 yearsii, with a parallel growth in their market shareiii. These ascending trends are justified by novel opportunities offered by biologics in multiple medical sectors where small molecules have either been ineffective or displayed severe side effects. The largest impact of biologics has been obtained in oncology, with more than 20 monoclonal antibodies (mAbs) routinely applied in the treatment of several types of canceriv. Moreover, the use of chimeric antigen receptor (CAR) T cells (see Glossary) offers – for the first time – a safe alternative to chemotherapy for patients affected by leukemia and lymphomas [1.Melenhorst J.J. et al.Decade-long leukaemia remissions with persistence of CD4+ CAR T cells.Nature. 2022; 602: 503-509Crossref PubMed Scopus (100) Google Scholar]. Biologics in the form of gene therapy products have provided the first therapeutic option for previously incurable monogenic diseases such as inherited blindnessv and spinal muscular atrophyvi. Finally, cell therapy has progressed remarkably over the past decade in the field of regenerative medicine, particularly for skin and cornea regenerationvii. This offers a unique opportunity to treat large burns, in addition to possible combination with gene therapy in the treatment of life-threating hereditary diseases such as epidermolysis bullosa [2.Kueckelhaus M. et al.Transgenic epidermal cultures for junctional epidermolysis bullosa – 5-year outcomes.N. Engl. J. Med. 2021; 385: 2264-2270Crossref PubMed Scopus (12) Google Scholar]. It is thus surprising that biological drugs, which stand to be game changers in providing therapy for otherwise incurable diseases in other medical sectors, struggle to tackle CVDs, which still represent the leading cause of death globallyviii. At present, CVDs are largely treated with small molecules that offer palliative support and preserve residual organ function [3.McDonagh T.A. et al.2021 ESC guidelines for the diagnosis and treatment of acute and chronic heart failure.Eur. Heart J. 2021; 42: 3599-3726Crossref PubMed Scopus (1938) Google Scholar], but cannot interfere with the complex mechanisms of disease onset and progression. Over the past 5 years, multiple studies have assessed the efficacy of biologics in inducing six major biological processes that might transform the current capacity to cure patients affected by CVDs. These comprise: (i) inducing cardioprotection; (ii) promoting angiogenesis; (iii) inhibiting excessive fibrosis; (iv) improving contractility; (v) reducing major risk factors (i.e., atherosclerosis); and, in the best possible scenario, (vi) stimulating cardiac regeneration (Figure 1). While encouraging results have been obtained in small-animal models of CVDs [4.Cannata A. et al.Gene therapy for the heart lessons learned and future perspectives.Circ. Res. 2020; 126: 1394-1414Crossref PubMed Scopus (39) Google Scholar], most of these approaches have essentially failed once they have reached either the large-animal or clinical stage [4.Cannata A. et al.Gene therapy for the heart lessons learned and future perspectives.Circ. Res. 2020; 126: 1394-1414Crossref PubMed Scopus (39) Google Scholar]. We believe that delineating the reasons for these failures will be valuable in developing solutions to overcome the existing limitations and thus to increase the chance of success of future research and clinical studies assessing the safety and efficacy of novel biological drugs for cardiac disease. Here, we describe the few biologics that have been developed in the cardiovascular field over the past 4 years, which have either entered the clinical arena or have been tested in large animals and are therefore expected to soon reach human application. These include recombinant proteins and mAbs, and gene and cell therapy products as detailed in the following subsections. Recombinant proteins have been the first type of biological drugs considered for use in the therapy of patients affected by heart disease. Starting from the pioneering studies led by Jeffrey Isner aimed at infusing angiogenic proteins to induce angiogenesis as a treatment for cardiac ischemia, many trials have delivered recombinant growth factors to the heart, with the aim of either exerting cardioprotection or inducing bone marrow (BM) cell mobilization [5.White S.J. Chong J.J.H. Growth factor therapy for cardiac repair: an overview of recent advances and future directions.Biophys. Rev. 2020; 12: 805-815Crossref PubMed Scopus (9) Google Scholar]. Most of these trials did not achieve successful results, as it soon became evident that the half-life of recombinant proteins in vivo is too short to result in any persistent therapeutic effect [6.Giacca M. Zacchigna S. VEGF gene therapy: therapeutic angiogenesis in the clinic and beyond.Gene Ther. 2012; 19: 622-629Crossref PubMed Scopus (183) Google Scholar]. Thus, it is unsurprising that only a few additional trials have started in recent years. Among these, the Randomised Trial Evaluating the Safety and Efficacy of a Single Low Dose of Intracoronary Insulin-like Growth Factor-1 Following Percutaneous Coronary Intervention for ST-Elevation Acute Myocardial Infarction (RESUS-AMI) Phase 1 study entailed the administration of insulin-like growth factor 1 (IGF1) in 47 patients with ST elevation myocardial infarction (STEMI) after percutaneous coronary intervention, without achieving significant improvement in cardiac function [7.Caplice N.M. et al.Randomized placebo controlled trial evaluating the safety and efficacy of single low-dose intracoronary insulin-like growth factor following percutaneous coronary intervention in acute myocardial infarction (RESUS-AMI).Am. Heart J. 2018; 200: 110-117Crossref PubMed Scopus (12) Google Scholar]. A new Phase 3 trial to assess the efficacy of systemic infusion of neuregulin (NRG) in chronic heart failure (HF) patients currently aims to enroll 1600 patients, despite the negative results obtained by similar approaches over the past 15 years (NCT03388593). More promisingly, the mobilization of hematopoietic cells using recombinant proteins such as granulocyte colony-stimulating factor (G-CSF) is expected to work systemically. Two recent publications support the efficacy of the early administration of G-CSF after acute myocardial infarction (AMI) in improving cardiac function for up to 10 years [8.Achilli F. et al.G-CSF for extensive STEMI.Circ. Res. 2019; 125: 295-306Crossref PubMed Scopus (19) Google Scholar,9.Leone A.M. et al.The effects of granulocyte colony-stimulating factor in patients with a large anterior wall acute myocardial infarction to prevent left ventricular remodeling: a 10-year follow-up of the RIGENERA Study.J. Clin. Med. 2020; 9: 1214Crossref Scopus (4) Google Scholar]. How these positive data compare with the discouraging results of intracardiac delivery of BM cell therapy in the heart remains an open question and suggests that complex cardioprotective mechanisms, on top of a direct contribution to cardiac repair, are relevant. mAbs constitute a special class of recombinant proteins. Due to their safety, specificity, and efficient manufacture, mAbs stand to be game changers for multiple disorders, including cancer and infectious and autoimmune diseases [10.Yasunaga M. Antibody therapeutics and immunoregulation in cancer and autoimmune disease.Semin. Cancer Biol. 2020; 64: 1-12Crossref PubMed Scopus (54) Google Scholar]. However, their application in the cardiovascular field remains in its infancy and is largely directed at blunt excessive inflammation in patients affected by AMI and HF. In the Canakinumab Anti-Inflammatory Thrombosis Outcomes Study (CANTOS) trial, a mAb specific for IL-1β reduced major adverse cardiovascular events (MACEs) in patients with a history of AMI [11.Everett B.M. et al.Inhibition of interleukin-1β and reduction in atherothrombotic cardiovascular events in the CANTOS trial.J. Am. Coll. Cardiol. 2020; 76: 1660-1670Crossref PubMed Scopus (52) Google Scholar]. Additional Phase 3 studies using mAbs targeting IL-6 (tocilizumab), CD20 (rituximab), and phosphorylcholine (ATH3G10) are currently ongoing (NCT03004703; NCT03332888; NCT03991143) [12.Sanchez-Trujillo L. et al.Phase II clinical trial testing the safety of a humanised monoclonal antibody anti-CD20 in patients with heart failure with reduced ejection fraction, ICFEr-RITU2: study protocol.BMJ Open. 2019; 9e022826Crossref PubMed Scopus (11) Google Scholar]. In addition to these strategies directed at the heart itself, a few approaches try to address major risk factors for cardiac diseases, such as hypercholesterolemia. Among these are the delivery of recombinant apolipoprotein A1 [13.Gibson C.M. et al.Rationale and design of ApoA-I Event Reducing in Ischemic Syndromes II (AEGIS-II): a Phase 3, multicenter, double-blind, randomized, placebo-controlled, parallel-group study to investigate the efficacy and safety of CSL112 in subjects after acute myocardial infarction.Am. Heart J. 2021; 231: 121-127PubMed Google Scholar] and the use of a mAb against proprotein convertase subtilisin/kexin type 9 (PCSK9), which effectively reduced MACEs in high-risk patients [14.Ma W. et al.Meta-analysis of randomized clinical trials comparing PCSK9 monoclonal antibody versus ezetimibe/placebo in patients at high cardiovascular risk.Atherosclerosis. 2021; 326: 25-34Abstract Full Text Full Text PDF PubMed Scopus (5) Google Scholar]. The EVOlocumab in Stable Heart Failure with Reduced Ejection Fraction of Ischemic Etiology (EVO-HF) clinical trial (NCT03791593) will specifically assess whether patients with HF with reduced ejection fraction (EF) (HFrEF) also benefit from PCSK9 inhibition. While gene therapy is becoming the treatment of choice for several genetic conditions, two gene therapy products have reached clinical approval and the market phase in the CVD sector. Glybera® was the world's first gene therapy product, approved in 2012 for patients affected by lipoprotein lipase deficiency, which leads to hypercholesterolemia and thus increases the risk of MACEs [15.Yla-Herttuala S. Endgame: Glybera finally recommended for approval as the first gene therapy drug in the European Union.Mol. Ther. 2012; 20: 1831-1832Abstract Full Text Full Text PDF PubMed Scopus (297) Google Scholar]. This, however, was one of the most expensive medicines in history (US$1 million per dose) and was withdrawn in 2017 for lack of demand [16.Senior M. After Glybera's withdrawal, what's next for gene therapy?.Nat. Biotechnol. 2017; 35: 491-492Crossref PubMed Scopus (57) Google Scholar]. The other product is Collategene®, a DNA plasmid encoding hepatocyte growth factor (HGF), delivered not to the heart but to patients affected with critical limb ischemia with the aim of inducing angiogenesis and thus favoring ulcer healing. Collategene® has received conditional and time-limited approval restricted to Japan [17.Shigematsu H. et al.Randomized, double-blind, placebo-controlled clinical trial of hepatocyte growth factor plasmid for critical limb ischemia.Gene Ther. 2010; 17: 1152-1161Crossref PubMed Scopus (155) Google Scholar]. Two new clinical trials are scheduled to start in the coming years aimed at evaluating the efficacy of an adenoviral vector expressing HGF in patients with AMI (NCT02844283; NCT03404024). Despite these two relative successes, an enormous effort has been made over the past 20 years in the development of gene therapy approaches targeting the myocardium, with the aim of either inducing new blood vessel formation in the ischemic heart or improving cardiac contractility. Both strategies have reached the clinical phase, with over 150 trials of therapeutic angiogenesis, all unsuccessful, and tens of studies aiming to improve cardiac contractility in HF patients. In this latter case, the main strategy for intervention was the delivery of an adeno-associated vector (AAV) for the expression of the calcium pump sarco/endoplasmic reticulum Ca2+-ATPase (SERCA)2A, which is known to be consistently downregulated in failing hearts [18.Zacchigna S. et al.Adeno-associated virus vectors as therapeutic and investigational tools in the cardiovascular system.Circ. Res. 2014; 114: 1827-1846Crossref PubMed Scopus (89) Google Scholar]. However, none of these studies has so far provided positive and conclusive results. As the failure of AAV-SERCA2A gene therapy could be reasonably attributed to either the inclusion of patients with multiple forms of HF or the presence of pre-existing anti-AAV antibodies, two new trials are ongoing to assess the efficacy of AAV-SERCA2A specifically in patients affected by HfrEF and the use of a heart-specific chimeric AAV mutant, which is supposed to be more resistant to neutralizing antibodies. Over the past 10 years, applications of gene therapy in cardiac diseases have extended beyond the transfer of cDNAs to embrace RNA-based therapies, including the delivery of long noncoding RNAs (lncRNAs), circular RNAs (circRNAs), miRNAs, short hairpin RNAs (shRNAs), small interfering RNAs (siRNAs), and locked nucleic acids (LNAs) [19.Bar C. et al.Non-coding RNAs: update on mechanisms and therapeutic targets from the ESC Working Groups of Myocardial Function and Cellular Biology of the Heart.Cardiovasc. Res. 2020; 116: 1805-1819Crossref PubMed Scopus (17) Google Scholar]. The success story of the long-acting first-in-class siRNA-based drug inclisiran targeting PCSK9, a protein involved in the regulation of low-density lipoprotein cholesterol (LDL-C) metabolism, represents a blockbuster in the field. The drug is entering the European market for adults with primary hypercholesterolemia [20.Lamb Y.N. Inclisiran: first approval.Drugs. 2021; 81: 389-395Crossref PubMed Scopus (76) Google Scholar] based on data from Phase 3 ORION studies [21.Raal F.J. et al.Inclisiran for the treatment of heterozygous familial hypercholesterolemia.N. Engl. J. Med. 2020; 382: 1520-1530Crossref PubMed Scopus (255) Google Scholar]. Inclisiran can reduce LDL-C levels by approximately 50% compared with placebo and is expected to impact, in particular, the coronary atherosclerotic burden in these patients. Regarding direct heart delivery, the only clinical trial so far conducted in this field aimed to antagonize miR-132 in HF patients [22.Taubel J. et al.Novel antisense therapy targeting microRNA-132 in patients with heart failure: results of a first-in-human Phase 1b randomized, double-blind, placebo-controlled study.Eur. Heart J. 2021; 42: 178-188Crossref PubMed Scopus (85) Google Scholar]. While the trial confirmed the feasibility and safety of the approach, evidence of efficacy is still missing. Additional approaches using RNA therapeutics have shown efficacy in large animals, mainly in pig models of ischemia reperfusion injury, which well mimic the human condition; for example, an anti-miRNA-21 LNA suppressed cardiac hypertrophy and improved cardiac function [23.Hinkel R. et al.AntimiR-21 prevents myocardial dysfunction in a pig model of ischemia/reperfusion injury.J. Am. Coll. Cardiol. 2020; 75: 1788-1800Crossref PubMed Scopus (50) Google Scholar] at 1 month after AMI. Even more exciting results were obtained using RNA drugs with the potential to promote cardiomyocyte proliferation and thus cardiac regeneration. These include the AAV-mediated delivery of either human miRNA-199a or a shRNA specific for the Hippo pathway Salvador (Sav) gene, which resulted in both massive cardiomyocyte proliferation and the generation of new myocardium in the ischemic pig heart [24.Gabisonia K. et al.MicroRNA therapy stimulates uncontrolled cardiac repair after myocardial infarction in pigs.Nature. 2019; 569: 418-422Crossref PubMed Scopus (219) Google Scholar,25.Liu S. et al.Gene therapy knockdown of Hippo signaling induces cardiomyocyte renewal in pigs after myocardial infarction.Sci. Transl. Med. 2021; 13eabd6892Crossref Scopus (21) Google Scholar]. More than 200 clinical trials of cell therapy for cardiac diseases, in particular for AMI, and nearly 50 meta-analyses have been performed over the past 20 years [26.Banerjee M.N. et al.Clinical studies of cell therapy in cardiovascular medicine: recent developments and future directions.Circ. Res. 2018; 123: 266-287Crossref PubMed Scopus (97) Google Scholar]. Most of these have assessed the efficacy of mesenchymal stromal cells (MSCs) despite unclear evidence of their mechanism of action, which could include anti-inflammatory, antiapoptotic, antifibrotic, and proangiogenic activities. Only a few of these trials reached the end of the study and gave conclusive results, mainly because of the small number of participants. The last metanalysis considered 38 randomized controlled trials involving 1907 participants who received BM-derived stem/progenitor cell therapy for cardiac repair and concluded that these cells do not provide any significant benefit to patients [27.Fisher S.A. et al.Cell therapy for heart disease: trial sequential analyses of two Cochrane reviews.Clin. Pharmacol. Ther. 2016; 100: 88-101Crossref PubMed Scopus (23) Google Scholar]. Against this background, two large randomized, double-blind, placebo-controlled trials were performed over the past 4 years and entailed the intracardiac delivery of BM-derived MSCs in patients with advanced, ischemic HF [New York Heart Association (NYHA) functional classification II/III]. The MSC-HF trial recruited 55 patients and showed an increase in left ventricle EF by 6% in the MSC group compared with placebo but no changes in NYHA class [28.Mathiasen A.B. et al.Bone marrow-derived mesenchymal stromal cell treatment in patients with ischaemic heart failure: final 4-year follow-up of the MSC-HF trial.Eur. J. Heart Fail. 2020; 22: 884-892Crossref PubMed Scopus (43) Google Scholar]. More recently, the Combination of Mesenchymal and c-kit+ Cardiac Stem Cells as Regenerative Therapy for Heart Failure (CONCERT-HF) study enrolled 125 patients and showed improved quality of life and a decline in hospitalization for HF in those who received MSCs either alone or in combination with c-kit+ cardiac cells, but no changes in either left ventricle EF or scar size [29.Bolli R. et al.A Phase II study of autologous mesenchymal stromal cells and c-kit positive cardiac cells, alone or in combination, in patients with ischaemic heart failure: the CCTRN CONCERT-HF trial.Eur. J. Heart Fail. 2021; 23: 661-674Crossref PubMed Scopus (30) Google Scholar]. These results led to additional skepticism on the real therapeutic relevance of this approach for patients affected by ischemic HF, as one would expect that an effective treatment invariably results in a clear improvement in both cardiac function and symptoms in multiple patient populations. These inconsistencies could be due, at least in part, to the use of autologous versus allogenic cells in the MSC-HF and CONCERT trials, respectively. While autologous cells have a safer profile in terms of engraftment and survival, the use of allogenic cells, which are potentially younger, could lead to better and more reproducible results [30.Zhang J. et al.Basic and translational research in cardiac repair and regeneration: JACC state-of-the-art review.J. Am. Coll. Cardiol. 2021; 78: 2092-2105Crossref PubMed Scopus (16) Google Scholar]. An interesting suitable target for cardiac cell therapy is represented by the niche of patients with severe ischemic heart disease experiencing refractory angina. Available evidence suggests functional and clinical benefits of BM-derived mononuclear or CD34+ cells when they are delivered intramyocardially into the ischemic territories of the left ventricle [31.Davies A. et al.Management of refractory angina: an update.Eur. Heart J. 2021; 42: 269-283Crossref PubMed Scopus (13) Google Scholar]. Beside the use of BM-MSCs, in the past few years encouraging results were obtained with pluripotent stem cells, both embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) to treat severe HF [32.Gao L. et al.Large cardiac muscle patches engineered from human induced-pluripotent stem cell-derived cardiac cells improve recovery from myocardial infarction in swine.Circulation. 2018; 137: 1712-1730Crossref PubMed Scopus (224) Google Scholar,33.Tiburcy M. et al.Defined engineered human myocardium with advanced maturation for applications in heart failure modeling and repair.Circulation. 2017; 135: 1832-1847Crossref PubMed Scopus (324) Google Scholar]. Transplantation of Human Embryonic Stem Cell-derived Progenitors in Severe Heart Failure (ESCORT) was the first clinical trial to assess the safety of the transplantation of cardiac-committed progenitor cells derived from human ESCs [34.Menasche P. et al.Transplantation of human embryonic stem cell-derived cardiovascular progenitors for severe ischemic left ventricular dysfunction.J. Am. Coll. Cardiol. 2018; 71: 429-438Crossref PubMed Scopus (237) Google Scholar]. At 1-year follow-up, the procedure was found to be safe, without any arrhythmias or evidence of tumor formation. More recently, three studies are using iPSC-derived cardiomyocytes to promote remuscularization and enhancement of myocardial performance in the failing heart (NCT04696328; NCT04945018; NCT04396899). As highlighted in the preceding text, the impact of biologics in the therapy of heart disease remains limited (Figure 2). This raises two important questions. First, why is this so, despite the high incidence and mortality of these diseases and thus the huge clinical and societal demand for innovative therapies? Second, what are the opportunities that may derive from understanding the struggle faced by past and current approaches? A partial explanation could reside in the intrinsic limits of biologics, such as the high costs and complex infrastructure and manufacture required for their production, which often limit their scalability for the treatment of large numbers of patients. However, mAbs are widely applied to myriad cancer patients [35.Jin S. et al.Emerging new therapeutic antibody derivatives for cancer treatment.Signal Transduct. Target. Ther. 2022; 7: 39Crossref PubMed Scopus (27) Google Scholar], and during the COVID pandemic we have witnessed the accelerated development and market uptake of numerous biologics (i.e., both adenoviral vectors and mRNA-based vaccines, SARS-CoV2-specific mAbs) [36.Corti D. et al.Tackling COVID-19 with neutralizing monoclonal antibodies.Cell. 2021; 184: 3086-3108Abstract Full Text Full Text PDF PubMed Scopus (132) Google Scholar,37.Tregoning J.S. et al.Progress of the COVID-19 vaccine effort: viruses, vaccines and variants versus efficacy, effectiveness and escape.Nat. Rev. Immunol. 2021; 21: 626-636Crossref PubMed Scopus (345) Google Scholar]. A recent analysis came to the counterintuitive conclusion that the median, total, premarket development time does not differ between biologic and small-molecule drugs and appears to be even shorter for biologic drugs using the Merck Index (10.6 vs 12.6 years) [38.Beall R.F. et al.Pre-market development times for biologic versus small-molecule drugs.Nat. Biotechnol. 2019; 37: 708-711Crossref PubMed Scopus (20) Google Scholar]. Thus, some peculiar features of cardiac diseases probably limit the application of biologics specifically for the heart. First, cardiac diseases are currently treated with safe and cost-effective drugs and thus the move to biological drugs could be less willingly accepted compared with cancer, for which chemotherapeutics are usually more expensive and fraught with major side effects [39.Schirrmacher V. From chemotherapy to biological therapy: a review of novel concepts to reduce the side effects of systemic cancer treatment (review).Int. J. Oncol. 2019; 54: 407-419PubMed Google Scholar]. Similar considerations could be applied to immune diseases, for which we do not have many therapies other than steroids, again causing several side effects [40.Fugger L. et al.Challenges, progress, and prospects of developing therapies to treat autoimmune diseases.Cell. 2020; 181: 63-80Abstract Full Text Full Text PDF PubMed Scopus (68) Google Scholar]. In addition, cardiac diseases are rather complex, depending on the coordinated action of multiple factors that cooperate in space and time in both disease onset and progression [41.Doran S. et al.Multi-omics approaches for revealing the complexity of cardiovascular disease.Brief. Bioinform. 2021; 22bbab061Crossref Scopus (11) Google Scholar]. Thus, the definition of the most relevant targets is a major challenge. Despite numerous attempts to use gene therapy to interfere with the pathogenesis of complex disorders, not only in the cardiovascular field but also in neurodegeneration, its success remains limited to genetic conditions such as severe immunodeficiencies, hemophilia, and hereditary blindness, in which the therapeutic gene is well defined and the only one required to cure the disease [42.Rittie L. et al.The landscape of early clinical gene therapies outside of oncology.Mol. Ther. 2019; 27: 1706-1717Abstract Full Text Full Text PDF PubMed Scopus (13) Google Scholar]. Similarly, cell therapy works well when stem cells are implanted in the same organ from which they are derived (i.e., hematopoietic stem cell transplantation to treat immune diseases, epithelial stem cells to regenerate the skin or the cornea [43.Malmegrim K.C.R. et al.Autologous hematopoietic stem cell transplantation for autoimmune diseases: from mechanistic insights to biomarkers.Front. 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Res. 2017; 120: 400-406Crossref PubMed Scopus (57) Google Scholar]. In the specific case of the heart, extreme confusion has been created in the field by a plethora of unreliable studies, which claimed the potential of either BM cells or circulating progenitor cells to give rise to new blood vessels and new myocardium in response to local stimuli. While these concepts have been clearly questioned in more recent years, initial studies have led to several unsuccessful clinical trials, with an impressive loss of money and credibility [45.Cai C.L. Molkentin J.D. The elusive progenitor cell in cardiac regeneration: slip slidin' away.Circ.